This invention relates to the assembly of a wall mounted programmable device such as a thermostat. In particular, this invention relates to the assembly of a keyboard, a display and a printed circuit board within such a wall mounted programmable device. The mounting of keyboard and display elements relative to a printed circuit board within a programmable thermostat is extremely important since these are the elements which receive information, process information, and display information to the user of the thermostat. Various approaches have heretofore been taken to mounting these elements so that they are precisely registered relative to each other in the thermostat.
U.S. Pat. No. 4,295,180 discloses a particular approach to mounting display elements and a keyboard relative to a printed circuit board. In particular, this patent discloses a printed circuit board having display elements already mounted thereon. A keyboard includes structure which snaps over the display elements so as to physically locate the keyboard relative to the display elements. The structure which snaps over the display elements is a series of detent daggers which engage the edges of the display elements. The thus located keyboard is mounted to the printed circuit board by screws which pass through holes in the circuit board. The circuit board, including the display elements and keyboard, are furthermore snapped into a faceplate of the thermostat by detent daggers in the faceplate engaging edges of the keyboard.
The above approach to registering the keyboard, display elements and printed circuit board with respect to each other within a thermostat is a complex process requiring careful alignment of successive sets of detent daggers. It also does not completely eliminate the need to use threaded fasteners. It furthermore does not reveal how the display elements are mounted to the printed circuit board which itself could be somewhat challenging given the limited amount of area on the board for accommodating the display elements. It would be preferable to assemble the keyboard, display, and printed circuit board of a thermostat in a less complex way. It would also be preferable if the assembly could be done without employing any threaded fasteners.
The present invention provides a programmable device with a front panel housing having a plurality of locating elements formed therein which allow the mounting of a display, a keyboard unit and a printed circuit board with respect to each other . The front panel housing furthermore includes a latch which engages an edge of the display following placement of the display relative to certain locating elements formed in the front panel housing. The keyboard unit includes a plurality of depressible keys, which are inserted into specifically delineated openings within the housing. The specifically delineated openings within the housing are preferably deep walled openings that surround each depressible key for a substantial distance. The keyboard unit also preferably includes projecting tabs which extend over the display when the depressible keys are fully inserted into the delineated holes. A printed circuit board having electrically conductive pads that make electrical contact with the depressible keys of the keyboard is placed over the keyboard and registered with respect to several locating elements formed around the periphery of the front panel housing. The printed circuit board snaps into place beneath certain raised elements formed in the periphery of the front panel housing. The display is thereafter preferably connected to the printed circuit board by a ribbon cable connector.
The front panel housing with the thus assembled display, keyboard unit and printed circuit board therein is aligned and snap fitted to a rear or back housing of the programmable device. A tab on one side of the front panel housing used in the snap fitting of the front panel housing to the rear housing can preferably be displaced or moved by a tool such as a bladed screwdriver so as to disengage this tab from the rear or back housing. This allows the front panel housing and the rear panel housing to be separated once again.